MFC r317214:

MFC r317214:

Turn off llvm/clang's ENABLE_BACKTRACES setting, since it never worked
properly anyway.  (Upstream has reorganized this somewhat in the mean
time, but for proper backtraces we would need llvm-symbolizer in base.)

MFC r317215:

Add function and data sections when building llvm, clang, lld and lldb,
and allow the linker to garbage collect them.  This shaves off up to a
few MB from the final executables.

git-svn-id: svn://svn.freebsd.org/base/stable/10@317599 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f